The invention pertains to treatment of pulp and mill waste water. In particular, the invention relates to treatment of the total waste water effluent from a pulp and paper mill for removal of colored constituents, such as lignins and degraded sugars, producing a neutral range pH effluent and a solid suitable for burning.
In the past, waste waters coming from the papermaking processes were decolored by treatment with chemicals to adjust their pH to between 2 and 5 before contacting them with an organic phase containing an amine insoluble in water. A water insoluble organophilic amine complex was formed containing the compounds of the organic matter and colored products in the waste water which thereupon were removed. See, for example U.S. Pat. No. 3,412,018 issued to Monzie on Nov. 19, 1968. Similarly, U.S. Pat. No. 4,089,780 to Svarz et al. (May 16, 1978) removed color from paper mill waste waters by treatment with a cationic water soluble polyamine having an average molecular weight of at least 300 at a pH of 2 to 5, followed by precipation with a water soluble anionic or nonionic organic polymer. Fuller, U.S. Pat. No. 3,740,363, removed colored bodies in a pretreatment stage by coagulation with alum in an acid solution and sedimentation of the coagulant in a gravity sedimentation clarifier. All of these past processes, while removing the color from waste water, left a highly acidic liquid which would damage the environment or require significant buffering, in order to be made suitable for release to the environment.
The removal of colored constituents has previously been done to papermaking waste water in order to recycle the colored constituents back to the papermaking processes. This treatment, referred to as a "pretreatment", as disclosed in applicant's co-pending U.S. patent application Ser. No. 711,238, filed Mar. 13, 1985, can only be used in treatment of certain concentrated streams of waste water from the pulp mill processes which have and undergone primary and secondary waste water treatment. Consequently, the "pretreatment" processes cannot be used to produce a neutral pH waste water having low enough concentration of colored bodies to allow release directly to the open environment.
Accordingly, it is an object of the present invention to provide a system for treatment of the entire pulp and paper mill waste water effluent which converts this waste water to a liquid containing a low concentration of colored bodies at a near neutral pH, and a solid suitable for burning in a furnace or recycle to the papermaking process.
It is another object of the present invention to provide a system and a method for decoloring waste water, removing insoluble BOD, phosphates and hydrogen sulfide.
It is another object of the present invention to provide a system and a method for removing colored bodies from the the waste water in a manner that said colored bodies are removed as a solid suitable for burning in a furnace.
It is yet another object of the invention to recover part of the originally added coagulant from the treated waste water, thus enabling reuse of the coagulum and reductions in overall cost of waste water treatment.
The foregoing and other objects, features, and advantages of this invention will be apparent from the following description and illustrations of the preferred embodiment of this invention.